1. Field of the Invention
The present invention relates to a device for picking up bone-conducted sound in the external auditory meatus and a communication device using the same.
2. Description of the Related Art
Conventionally, in order to transmit speech in noisy places such as coal mining sites, quarrying sites, airports, construction sites, and sheet metal factories, a method in which a unidirectional microphone is used for the lips and a method in which an acceleration-type vibration pickup is used by being attached to the throat or the forehead have been adopted extensively. With the former unidirectional microphone, however, there are limitations in the elimination of external noise, and this method is therefore unsuitable for intensely noisy places. Meanwhile, in the latter case, since the vibration pickup needs to be closely secured to the throat or the forehead, there have been drawbacks in that the attachment thereof is complicated or troublesome, that the vibration pickup, when fitted, does not make a good appearance, and that a sensation of a foreign object being attached or discomfort in use felt by the user is so conspicuous that it cannot withstand a long time of use.
Accordingly, the present inventor has proposed in Japanese Patent Publication No. 39763/1978 a device for picking up bone-conducted sound vibrations from the wall of the external auditory meatus by disposing a vibration pickup in an earpiece forming a tubular casing for insertion into the external auditory meatus of the ear, the operating direction of the vibration pickup being substantially orthogonal to the direction of the external auditory meatus.
With the above-described pickup device, however, the earpiece constituting the tubular casing is difficult to be held stably unless it is inserted sufficiently deeply in the external auditory meatus. Therefore, if the earpiece is inserted sufficiently, the contact area and the contact pressure with respect to the external auditory meatus increase. This is favorable for the improvement of the function of the device, but the earpiece is applied too tightly in the external auditory meatus, so that a sensation of a foreign object being attached or discomfort is imparted to the user. In addition, the contact pressure becomes too high for some people, who come to have a sensation of pressure or a sensation of the external auditory meatus being blocked.
In addition, as another conventional device, a compact two-way communication device is known which incorporates an earphone unit in a portion thereof which is formed integrally with a tubular casing having a built-in microphone unit of the above-described type, so as to permit communication. With such a device, however, since the microphone unit and the earphone unit are formed integrally and are disposed in proximity to each other, there are cases where the sound pressure from the earphone unit is transmitted circuitously to the microphone unit. For the purpose of controlling the same, a method is adopted in which the earphone unit is surrounded by a sound absorbing material or a vibration absorbing material. However, if the external noise becomes large, the sound pressure in the earphone unit is inevitably increased, with the result that there has been the drawback that the circuitous transmission occurs and a howling is produced. Hence, this two-way communication device can be used only when the sound pressure in the earphone unit is set to a low level.
Air vibrations of sound from the earphone unit, external noise, and the like are, in principle, difficult to pick up by the vibration pickup-type external auditory meatus microphone, and the direction of air vibrations of external noise and the like and the direction of vibration of the external auditory meatus microphone unit are in an orthogonal relationship. Hence, the signal-to-noise (S/N) ratio of speech in the noise should naturally be high. This being the case, however, since the aforementioned microphone unit and the casing incorporating the earphone unit are formed integrally, the overall shape becomes large, and the vibration absorbing area increases, so that the external noise is picked up via the casing. Thus, there has been the drawback that although the vibration pickup type should exhibit an excellent anti-noise characteristic, the S/N ratio declines in a very noisy condition.